The present invention relates to a method for growing n-type crystals of the II-VI compound semiconductors containing sulfur.
With a metal organic vapor phase epitaxial growth method (hereinafter referred to as an MOVPE method) for the II-VI compound semiconductors, the use of hydrides (such as hydrogen sulfide, hydrogen selenide, etc.) as raw materials of the group VI elements permits the growth of crystals at as low a temperature as 300.degree. C. or so, and hence keeps the crystals from deterioration by temperature changes from growth temperature to room or ambient temperature. On the other hand, however, the hydrogen compound materials of the group VI elements react with organometallic materials of the group II elements (dialkyl cadmium, dialkyl zinc, etc.) even at low temperatures such as room temperature, and to avoid this, it is necessary to mix these raw materials at close vicinity of a semiconductor substrate one which the II-VI compound crystal is grown. This leads to scattering in the thicknesses, qualities, etc. of grown layers. As a solution to this problem, there has been proposed a crystal growth method which employs, raw materials of the group VI elements which do not react with the organometallic materials of the group II elements, alkyl compounds (diethl sulfur, dimethyl sulfur, tertiary butyl mercaptan, diethyl selenium, dimethyl selenium, ethyl selenol, etc.) which are organic compounds, and experiments on this method have also been conducted.
With the prior art described above, an organometallic material of the group III (trialkyl indium, trialkyl gallium, or the like) or organic material of the group/VII (alkyliodide, alkylbromide, or the like), which is used as a dopant for forming an n-type growth layer, reacts with the group II element materials at low temperatures, resulting in a serious reduction of the growth rate and deterioration of the growth layer. Moreover, due to the vapor pressure of the by-product indium gets mixed into a non-doped layer subsequently formed, and consequently, the carrier concentration of the non-doped layer does not decrease and the composition of the n-type layer differs from the intended value, resulting in the quality of the crystal being impaired.